Insulating layer next to fin structure and method of removing fin structure

ABSTRACT

A method of removing a fin structure includes providing a substrate. A fin structure extends from the substrate. A mask layer is disposed on a top surface of the fin structure. An organic dielectric layer covers the substrate, the fin structure and the mask layer. A first etching process is performed to entirely remove the mask layer by taking the organic dielectric layer as a mask. Then a second etching process is performed to remove the fin structure. The first etching process is preferably an anisotropic etching process, and the second etching process is an isotropic etching process.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method of removing a fin structure,and more particularly to a method of removing a fin structure by twodifferent etching processes.

2. Description of the Prior Art

Transistors, such as metal oxide semiconductor field-effect transistors(MOSFETs), are the core building block of the vast majority ofsemiconductor devices. Some semiconductor devices, such as highperformance processor devices, can include millions of transistors. Forsuch devices, scaling down the size of the transistors to thus increasetransistor density has traditionally been a high priority in thesemiconductor manufacturing industry. This scaling down process providesthe benefits of increased production efficiency and lowered associatedcosts.

Such scaling down, however, has also increased the complexity ofprocessing and manufacturing ICs. For the advantages of scaling down tobe fully realized, developments in IC processing and manufacturing areneeded. A three dimensional transistor, such as a fin-type field-effecttransistor (FinFET), has been introduced to replace a planar transistor.Existing FinFET devices and methods of fabricating FinFET devices,although adequate for their intended purposes, have not been entirelysatisfactory in all respects. For example, forming fin structures withdifferent densities raise challenges in FinFET process development. Inview of the above, it would be an advantage in the art to provide abetter method to form fin structures with different densities.

SUMMARY OF THE INVENTION

In one embodiment, an insulating layer is provided next to a finstructure. The insulating layer includes a substrate, a first finstructure extending and protruding from the substrate, a recess embeddedin the substrate and adjacent to the first fin structure, and aninsulating layer disposed on the substrate, which contacts the first finstructure and fills in the recess.

In another embodiment, a method of removing a fin structure includes thesteps of providing a substrate, and providing a fin structure extendingfrom the substrate. A mask layer is disposed on a top surface of the finstructure, and an organic dielectric layer covers the substrate, the finstructure and the mask layer. Later, the organic dielectric layer ispatterned so an opening is formed on the organic dielectric layer,wherein the mask layer is exposed by the opening. Subsequently, a firstetching process is performed to entirely remove the mask layer by takingthe organic dielectric layer as a mask. Finally, a second etchingprocess is performed to remove the fin structure.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 5 depict a method of removing a fin structure accordingto a preferred embodiment of the present invention, wherein:

FIG. 1 depicts a stage of providing a substrate with numerous finstructures;

FIG. 2 is a fabricating stage following FIG. 1;

FIG. 3 is a fabricating stage following FIG. 2;

FIG. 4 is a fabricating stage following FIG. 3;

FIG. 5 is a fabricating stage following FIG. 4.

FIG. 6 depicts an insulating layer next to a fin structure.

FIG. 7 depicts a method of removing a fin structure according to anotherpreferred embodiment of the present invention.

FIG. 8 depicts a recess in a triangular profile.

DETAILED DESCRIPTION

Based on different product requirements, fin structures in differentregions will often be arranged in different densities. In other words,fin structures are closer to each other in a high density region, andare farther from each other in a low density region. The fabricatingsteps of fin structures include etching the substrate. If, however, finstructures in the high density region and in the low density region areformed by a single etching step, the shape of the resultant finstructures will not match the original design due to the loading effect.

To avoid this loading effect, the method of the present inventionspecially forms fin structures with the same density in all regions.Later, redundant fin structures in the low density region are removed bytwo different etching processes. In detail, a dry etching process isutilized to remove a mask layer on the fin structure and then a wetetching process removes the entire fin structure. In some circumstances,part of the fin structure is removed in the dry etching process alongwith the mask layer. If the redundant fin structures are removed by onlythe dry etching process, an organic dielectric layer covering wanted finstructures adjacent to the redundant fin structures will be removedentirely before the dry etching process is over, causing the wanted finstructures to undergo a dry etch as they are not protected by theorganic dielectric layer. By using the two step etching process of thepresent invention, the wanted fin structures will not be damaged duringthe removal of the redundant fin structures.

FIG. 1 to FIG. 5 depict a method of removing a fin structure accordingto a preferred embodiment of the present invention. As shown in FIG. 1,a substrate 10 is provided. The substrate 10 the present invention maybe a bulk silicon substrate, a germanium substrate, a gallium arsenidesubstrate, a silicon germanium substrate, an indium phosphide substrate,a gallium nitride substrate or a silicon carbide substrate. At least afin structure 12 extends and protrudes from the substrate 10. The numberof fin structures 12 may be single or plural, and is exemplified as fourin the present invention. The fin structures 12 are further divided intotwo first fin structures 14 and two second fin structures 16 based onwhether the fin structures 12 will be removed or not, wherein the firstfin structures 14 will be preserved, and the second fin structures 16will be removed. The first fin structures 14 and the second finstructures 16 are disposed alternately. The number of the first finstructures 14 and the second fin structures 16 can be altered based ondifferent requirements. The first fin structures 14 and the second finstructures 16 are the same in their material and structure. Therefore,only the material and structure of the second fin structures 16 will bedescribed in the following description. The material of each of thesecond fin structures 16 is the same as the material of the substrate10. For example, if the substrate 10 is made of silicon, the second finstructures 16 are made of silicon as well. Each second fin structure 16includes a top surface 18. The top surface 18 is the highest surface ofthe second fin structure 16 with respect to the top surface of thesubstrate 10. A mask layer 20 is disposed on and contacts the topsurface 18 of each of the second fin structures 16. A mask layer 20 isalso disposed on each of the first fin structures 14. The mask layer 20may be made of single or multiple materials. The mask layer 20 mayinclude silicon nitride, silicon oxide or silicon oxynitride. In thisembodiment, the mask layer 20 is formed by a silicon oxide layer 22 anda silicon nitride layer 24. The silicon oxide layer 22 is below thesilicon nitride layer 24. Furthermore, a recess 26 is disposed betweenthe first fin structure 14 and the second fin structure 16 next to thefirst fin structure 14. A height H of each of the second fin structures16 is preferably 1200 angstroms. A width W of the recess 26 ispreferably smaller than 20 nanometers. An organic dielectric layer 28 isformed to entirely cover the substrate 10, the first fin structures 14and the second fin structures 16, wherein the organic dielectric layer28 fills up the recess 26. The organic dielectric layer 28 may containscarbon, hydrogen, and oxygen, but does not contain silicon. The organicdielectric layer 28 is preferably made of homogeneous andnon-photosensitive material. Because of the property of the organicdielectric layer 28, the organic dielectric layer 28 can be formed onthe substrate 10, the first fin structures 14, and the second finstructures 16 by a spin coating process. In this way, the organicdielectric layer 28 can entirely fill up the recess 26 and have a flattop surface.

A silicon-containing bottom anti-reflective coating 30 and a photoresistlayer 32 are formed to cover the organic dielectric layer 28. Later, thephotoresist layer 32 is patterned to form at least one opening 34 withinthe photoresist layer 32. In this embodiment, the number of openings 34is exemplified as two. As shown in FIG. 2, the silicon-containing bottomanti-reflective coating 30 and the organic dielectric layer 32 arepatterned by taking the photoresist layer 32 as a mask to form at leastone opening 36 on the organic dielectric layer 28. Because thephotoresist layer 32 serves as the mask when patterning thesilicon-containing bottom anti-reflective coating 30 and the organicdielectric layer 32, the number of openings 36 should be the same as thenumber of openings 34. The mask layer 20 on each of the second finstructures 16 is exposed through the corresponding opening 36.Therefore, one mask layer 20 is exposed through one opening 36. Theorganic dielectric layer 28 can be patterned by a dry etching process.During the dry etching process, the photoresist layer 32 and thesilicon-containing bottom anti-reflective coating 30 are consumedentirely. The etchant in the dry etching process can be hydrogenbromide, chlorine gas or fluorine-containing gas.

As shown in FIG. 3, a first etching process 38 is performed by takingthe organic dielectric layer 28 as a mask to entirely remove the exposedmask layers 20. The first etching process 38 is preferably ananisotropic etching process such as a dry etching process. The etchantused in the first etching process 38 may be a fluorine-containing gas.After removing the mask layers 20, the second fin structures 16 areexposed through the openings 36. According to another preferredembodiment of the present invention, after removing the mask layers 20entirely, the first etching process 38 can continue to etch the secondfin structures 16. This is shown in FIG. 7. For example, one third ofthe height H of each of the second fin structures 16 can be removed.

FIG. 4 continues from FIG. 3. As shown in FIG. 4, a second etchingprocess 40 is performed to entirely remove the second fin structures 16by taking the organic dielectric layer 28 as a mask. After removing thesecond fin structures 16, the second etching process 40 continues toetch part of the substrate 10 to form a recess 42 in the substrate 10.According to another preferred embodiment of the present invention, thesecond etching process 40 stops at the point that the second finstructures 16 are entirely removed. Therefore, no recess will be formedin the substrate 10. Subsequent figures and processes show the recess 42is formed in the substrate 10 as an example. The second etching process40 is preferably an isotropic etching process such as a wet etchingprocess or an isotropic dry etching process. If the second etchingprocess 40 is a wet etching process, the etchant can be an alkalinesolution or an acidic solution. If an alkaline solution is used, thesubstrate 10 will be etched along the lattice direction by the alkalinesolution to form the recess 42 in a hexagonal profile (as shown in FIG.4) or to form a recess 142 in a triangular profile (as shown in FIG. 8).If, however, an acidic solution is used or an isotropic dry etchingprocess is used, the substrate 10 will not be etched along the latticedirection. The recess will not form a hexagonal profile or a triangularprofile. The alkaline solution may be tetramethylammonium hydroxide(TMAH). It is noteworthy that the organic dielectric layer 28 stillcovers the substrate 10 while the second fin structures 16 are removed.

As shown in FIG. 5, the organic dielectric layer 28 is completelyremoved. At this point, the method of removing a fin structure of thepresent invention is completed. As shown in FIG. 6, an insulating layer(not shown) is formed to cover the substrate 10 and the first finstructures 14, and to fill in the recess 42. The insulating layer ispreferably silicon oxide. Later, the insulating layer is etched back toa predetermined height to form an insulating layer 44. The insulatinglayer 44 serves as a shallow trench isolation (STI) at both sides ofeach of the first fin structures 14. The shallow trench isolation fillsup the recess 42. After that, a gate dielectric layer, and a gateelectrode can be formed to cross the first fin structures 14. Later,source/drain doping regions can be formed at two sides of the gateelectrode in the first fin structures 14. Based on differentrequirements, the mask layer 20 on the first fin structures 14 can beremoved before forming the gate dielectric layer.

The position of the first fin structures 14 and the second finstructures 16 can be altered based on different requirements. The numberof the first fin structures 14, the number of the second fin structures16, and the total number of the first fin structures 14 and the secondfin structures 16 can also be altered. For example, there can be twofirst fin structures 14 arranged in sequence followed by two second finstructures 16 arranged in sequence That is, there will be two recesses42 side by side with no fin structure disposed between the two recesses42 after the etching processes. In another case, there can be two firstfin structures 14 and one second fin structure 16. In this way, onesecond fin structure 16 will be removed, while the two first finstructures 14 remain. In addition, the number of the recesses 42 isequal to the number of second fin structures 16.

FIG. 6 depicts an insulating layer next to a fin structure. As shown inFIG. 6, the insulating layer includes a substrate 10. A first finstructure 14 extends and protrudes from the substrate 10. The materialof the first fin structure 14 is the same as the material of thesubstrate 10. For example, if the substrate 10 is made of silicon, thefirst fin structure 14 is made of silicon as well. A recess 42 isembedded in the substrate 10. The recess 42 is adjacent to the first finstructure 14. The recess 42 has a hexagonal profile or a triangularprofile. An insulating layer 44 is disposed on the substrate 10,contacts the first fin structure 14 and fills in the recess 42. Anotherfirst fin structure 14 extends and protrudes from the substrate 10. Therecess 42 is disposed between the two first fin structures 14. Theinsulating layer 44 contacts both of the first fin structures 14. Theinsulating layer 44 includes silicon oxide. A mask layer 20 covers eachof the first fin structures 44. The mask layer 20 includes silicon oxidelayer 22 and silicon nitride layer 24 disposed from bottom to top.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method of removing a fin structure, comprising:providing a substrate, and a fin structure extending from the substrate,wherein a mask layer is disposed on a top surface of the fin structure,and an organic dielectric layer covers the substrate, the fin structureand the mask layer; patterning the organic dielectric layer to form anopening on the organic dielectric layer, wherein the mask layer isexposed by the opening; performing a first etching process to entirelyremove the mask layer by taking the organic dielectric layer as a mask,wherein part of the fin structure is removed during the first etchingprocess; and performing a second etching process to remove the finstructure.
 2. The method of removing a fin structure of claim 1, whereinone third of the fin structure is removed during the first etchingprocess.
 3. The method of removing a fin structure of claim 1, whereinthe second etching process further comprises: partly removing thesubstrate to form a recess in the substrate.
 4. The method of removing afin structure of claim 1, wherein the first etching process is ananisotropic etching process.
 5. The method of removing a fin structureof claim 4, wherein the first etching process is a dry etching process.6. The method of removing a fin structure of claim 1, wherein the secondetching process is an isotropic etching process.
 7. The method ofremoving a fin structure of claim 6, wherein the second etching processis a wet etching process or an isotropic dry etching process.